Detecting vulnerable plaque

ABSTRACT

An apparatus and associated method for detecting vulnerable plaque within a lumen defined by an intraluminal wall is described. The apparatus includes a probe having a distal portion and a proximal portion. The apparatus includes an optical waveguide extending along the probe. The optical waveguide is configured to carry optical radiation between the distal and proximal portions, and has a distal end in communication with the intraluminal wall. The apparatus includes an interferometer coupled to the optical waveguide and configured to provide an interference signal for sub-surface imaging of the intraluminal wall, and a processing module configured to provide spectroscopic information from detected intensity of light collected from the intraluminal wall.

FIELD OF INVENTION

The invention relates to devices for luminal diagnostics, and inparticular, to detecting vulnerable plaque.

BACKGROUND

Atherosclerosis is a vascular disease characterized by a modification ofthe walls of blood-carrying vessels. Such modifications, when they occurat discrete locations or pockets of diseased vessels, are referred to asplaques. Certain types of plaques are associated with acute events suchas stroke or myocardial infarction. These plaques are referred to as“vulnerable plaques.” A vulnerable plaque typically includes alipid-containing pool separated from the blood by a thin fibrous cap. Inresponse to elevated intraluminal pressure or vasospasm, the fibrous capcan become disrupted, exposing the contents of the plaque to the flowingblood. The resulting thrombus can lead to ischemia or to the shedding ofemboli.

One method of locating vulnerable plaque is to peer through the arterialwall with infrared light. To do so, one inserts a catheter through thelumen of the artery. The catheter includes a delivery fiber forilluminating a spot on the arterial wall with infrared light. A portionof the light penetrates the blood and arterial wall, scatters offstructures within the wall and re-enters the lumen. This re-entrantlight can be collected by a collection fiber within the catheter andsubjected to spectroscopic analysis. This type of diffuse reflectancespectroscopy can be used to determine chemical composition of arterialtissue, including key constituents believed to be associated withvulnerable plaque such as lipid content.

Another method of locating vulnerable plaque is to use optical coherencetomography (OCT) to image the arterial tissue surrounding the lumen. Touse this method, one also inserts a catheter through the lumen of theartery. The catheter includes a fiber that transports light having alimited coherence length through imaging optics to the arterial wall.The backscattered light couples back into the fiber towards aninterferometer. The interferometer provides a cross-correlation signalthat is used to map the shape of the arterial tissue. This map of themorphology of the arterial wall can be used to detect the fibrous capand other structural characteristics associated with vulnerable plaque.

SUMMARY

The invention is based on the recognition that combining two detectionmodalities, infrared spectroscopy and sub-surface imaging (e.g., OCT),in the same probe increases the probe's ability to detect lesions suchas vulnerable plaque.

In one aspect, the invention features an apparatus for detectingvulnerable plaque within a lumen defined by an intraluminal wall. Theapparatus includes a probe having a distal portion and a proximalportion. The apparatus includes an optical waveguide extending along theprobe. The optical waveguide is configured to carry optical radiationbetween the distal and proximal portions, and has a distal end incommunication with the intraluminal wall. The apparatus includes aninterferometer coupled to the optical waveguide and configured toprovide an interference signal for sub-surface imaging of theintraluminal wall, and a processing module configured to providespectroscopic information from detected intensity of light collectedfrom the intraluminal wall.

This aspect can include one or more of the following features.

The processing module is configured to receive the detected intensity oflight collected from the intraluminal wall by the optical waveguide.

The apparatus further includes a second optical waveguide extendingalong the probe, the second optical waveguide being configured to carryoptical radiation between the distal and proximal portions, and having adistal end in communication with the intraluminal wall.

The processing module is configured to receive the detected intensity oflight collected from the intraluminal wall by the second opticalwaveguide.

The interferometer is configured to provide an interference signal forsub-surface imaging by performing optical coherence tomography.

The interferometer is configured to provide an interference signal forsub-surface imaging by performing optical frequency domainreflectometry.

In another aspect, the invention features an apparatus for detectingvulnerable plaque within a lumen defined by an intraluminal wall. Theapparatus includes a probe having a distal portion and a proximalportion. The apparatus includes a first optical waveguide extendingalong the probe, the first optical waveguide being configured to carryoptical radiation between the distal and proximal portions, and having adistal end in communication with the intraluminal wall. The apparatusincludes a second optical waveguide extending along the probe, thesecond optical waveguide being configured to carry optical radiationbetween the distal and proximal portions, and having a distal end incommunication with the intraluminal wall. The apparatus includes a thirdoptical waveguide coupled to a portion of the second optical waveguide.

This aspect can include one or more of the following features.

The apparatus further includes an optical coupler in opticalcommunication with the distal end of the first optical waveguide, theoptical coupler being configured to transmit optical radiation betweenthe first optical waveguide and the intraluminal wall.

The apparatus further includes an optical coupler in opticalcommunication with the distal end of the second optical waveguide, theoptical coupler being configured to transmit optical radiation betweenthe second optical waveguide and the intraluminal wall.

The apparatus further includes a fourth optical waveguide coupled to aportion of the first optical waveguide.

The apparatus further includes a variable-delay coupler configured tocouple optical radiation from the third optical waveguide into thefourth optical waveguide with a variable optical group delay.

The variable-delay coupler is configured to scan the variable opticalgroup delay by an amount corresponding to a coherence length of a sourceof optical radiation.

The apparatus further includes an optical source configured to coupleoptical radiation into the second and third optical waveguides.

The apparatus further includes an optical detector configured to receiveoptical radiation from the first and fourth optical waveguides.

The apparatus further includes a variable-delay reflector configured toreverse the direction of propagation of optical radiation in the thirdoptical waveguide with a variable optical group delay.

The variable-delay reflector is configured to scan the variable opticalgroup delay by an amount corresponding to a coherence length of a sourceof optical radiation.

The apparatus further includes an optical source configured to coupleoptical radiation into the second and third optical waveguides; and afirst optical detector configured to receive optical radiation from thesecond and third optical waveguides.

The apparatus further includes a second optical detector configured toreceive optical radiation from the first optical waveguide.

The optical coupler can be an atraumatic light-coupler configured toatraumatically contact the intraluminal wall.

In another aspect, the invention features a method for detectingvulnerable plaque within a lumen defined by an intraluminal wall. Themethod includes inserting a distal portion of a probe into the lumen.The method includes providing optical radiation to the intraluminal wallthrough an optical waveguide extending along the probe. The methodincludes combining reference optical radiation with optical radiationscattered from the intraluminal wall, and returning through the opticalwaveguide, to provide an interference signal for sub-surface imaging ofthe intraluminal wall. The method includes processing a detectedintensity of light collected from the intraluminal wall to extractspectroscopic information.

As used herein, “infrared” means infrared, near infrared, intermediateinfrared, far infrared, or extreme infrared.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although methods and materialssimilar or equivalent to those described herein can be used in thepractice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

Other features and advantages of the invention will be apparent from thefollowing detailed description, and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A-1D are schematic diagrams of embodiments of a vulnerable plaquedetection system for identifying vulnerable plaque.

FIG. 2 is a schematic view of a probe in contact with the arterial wall.

FIG. 3 is a cross-section of the probe of FIG. 2.

FIGS. 4A-G are exemplary atraumatic light-couplers for an optical fiber.

FIGS. 5A-F are schematic views of single-probe spectroscopes.

FIGS. 6A-F are schematic views of multi-probe spectroscopes.

FIG. 7A is a schematic view of a probe emerging from a cannula having atapered distal end.

FIG. 7B is a schematic view of a probe emerging from a cannula having aflared distal end.

FIGS. 8A-8F are schematic views of multi-probe spectroscopes in whichthe atraumatic light-couplers are along the sides of the probes.

FIGS. 8G-K are schematic views of spectroscopes in which the probes areintegrated into the cannula.

FIGS. 9A-D are views of exemplary atraumatic light-couplers for theprobes in FIGS. 8A-H.

FIG. 10 is a view of an optical bench of an optical delivery andcollection head.

DETAILED DESCRIPTION

The vulnerability of a plaque to rupture can be assessed by detecting acombination of attributes such as macrophage presence, local temperaturerise, and a lipid-rich pool covered by a thin fibrous cap. Somedetection modalities are only suited to detecting one of theseattributes.

FIGS. 1A-1D show embodiments 100A-100D of a vulnerable plaque detectionsystem (VPDS) that combines two detection modalities for identifyingvulnerable plaque 102 in an arterial wall 104 of a patient. Thecombination of both chemical analysis, using infrared spectroscopy todetect lipid content, and morphometric analysis, using sub-surfaceimaging (e.g., optical coherence tomography (OCT) or optical frequencydomain reflectometry (OFDR)) to detect cap thickness, enables greaterselectivity in identifying potentially vulnerable plaques than eitherdetection modality alone.

Referring to FIG. 1A, in a first embodiment, a VPDS 100A includes aprobe 106 to be inserted into a selected artery, e.g. a coronary artery,of the patient. A first optical waveguide 108 (e.g., an optical fiber)extends between a distal end 110 and a proximal end 112 of the probe 106for collecting scattered optical radiation for spectroscopic analysis ofthe arterial wall 104. A second optical waveguide 114 also extendsbetween the distal end 110 and the proximal end 112 of the probe 106 andis part of an interferometer for sub-surface imaging of the arterialwall 104. Optical radiation for both sub-surface imaging andspectroscopic analysis is delivered to the arterial wall through thesecond optical waveguide 114. An optical delivery and collection head115 includes one or more optical couplers in optical communication withdistal ends of the first and second optical waveguides to couple lightfrom the arterial wall into the first and second optical waveguides, asdescribed in more detail below.

The interferometer for sub-surface imaging includes a beamsplitter 116that mixes the optical radiation from the second optical waveguide 114with optical radiation from a third optical waveguide 118. In thisembodiment, the beamsplitter 116 is a 50/50 fused-fiber 2×2 coupler witha 50% power splitting ratio, two input ports and two output ports.Alternatively, any of a variety of optical beam splitting andrecombining devices and techniques may be used. The second opticalwaveguide 114 includes an optical fiber with one end that extends intothe probe 106 and another end that is coupled (e.g., fusion spliced orbutt-coupled) to an optical fiber output port of the beamsplitter 116.The third optical waveguide 118 includes an optical fiber with one endthat is coupled to the other optical fiber output port of thebeamsplitter 116 and another end that is coupled to a variable-delayreflector 120 (e.g., a translatable mirror, a tiltable grating, atunable fiber loop, etc.) to reverse the direction of propagation ofoptical radiation in the third optical waveguide with a variable opticalgroup delay. Alternatively, either or both of the second and/or thirdoptical waveguides can have optical fibers that are integral with thebeamsplitter 116.

An optical source 122 provides infrared light that is coupled into thesecond and third optical waveguides via an optical coupler 124 that isin optical communication with a first optical fiber input port of thebeamsplitter 116. A first optical detector 126 is in opticalcommunication with a second optical fiber input port of the beamsplitter116, via an optical coupler 128, to receive optical radiation from thesecond and third optical waveguides (114 and 118). The optical radiationfields from the second and third optical waveguides sum to produce aninterference pattern of optical intensity at the first optical detector126. A second optical detector 130 is in optical communication with thefirst optical waveguide 108, via an optical coupler 132.

The first and second optical detectors each provide an electrical signalindicative of optical intensity to a processing module 134. Theprocessing module 134 converts this signal into digital data (e.g.,using an analog-to-digital (“A/D”) converter) that can be analyzed by adigital processor.

The intensity signal produced by the first optical detector 126 is usedfor sub-surface imaging. The processing module 134 extracts from thissignal sub-surface imaging information about the arterial wall 104.

The intensity signal produced by the second optical detector 130 is usedfor spectroscopic analysis. The processing module 134 can extractspectroscopic information from this intensity signal in any of a varietyof ways. For example, the processing module 134 can include a spectrumanalyzer to perform infrared spectroscopy.

Referring to FIG. 1B, in a second embodiment, a VPDS 100B includes thesecond and the third optical waveguides (114 and 118) of the VPDS 100A,but not the first optical waveguide 108. The VPDS 100B uses the opticalradiation coupled from the second and third optical waveguides for bothsub-surface imaging and spectroscopic analysis.

Both the first embodiment of the VPDS 100A and the second embodiment ofthe VPDS 100B use a Michelson Interferometer (MI) topology. In the MItopology, a beamsplitter 116 splits the incoming light into a“measurement arm” and a “reference arm.” Light in the measurement arm istransformed (e.g., in amplitude and/or phase) by scattering from ameasurement object (the arterial wall 104 in this example). Light in thereference arm undergoes a group delay (in some cases a variable delaydue to a path length change). Light from both arms recombines in thebeamsplitter 116 to produce an interference signal.

In the second embodiment, a reflector 121 can be a variable-delayreflector that provides a variable group delay for the light in thethird optical waveguide 118. This delayed light is combined with lightreturning through the second optical waveguide 114. In this case, aprocessing module 140 uses the envelope of the signal detected by thefirst optical detector 126 to extract information about the location ofstructural elements in the arterial wall 104 (i.e., sub-surfaceimaging). As the group delay of the reference arm is scanned, theinterference signal yields information from different depths of themeasurement object according to a coherence envelope of alimited-coherence light source (e.g., a broadband light source).Adittionally, the processing module 140 takes the Fourier-transform (FT)of the signal centered at a particular group delay to obtain thecumulative absorbance over a particular thickness of the arterial wall104 (i.e., spectroscopic information).

Alternatively, in the second embodiment, the reflector 121 can be astationary reflector and the processing module 140 can obtainsub-surface imaging information and spectroscopic information based oncombined properties of, for example, the optical source 122, the opticalcoupler 128, and the optical detector 126. For example, the source 122can emit narrowband radiation scanned over a range of wavelengths suchthat the optical coupler 128 and optical detector 126 generate aspectrally-resolved signal as a function of the scanned wavelength.Alternatively, the source 122 can emit broadband radiation including arange of wavelengths such that the optical coupler 128 and a“spectrally-sensitive” optical detector 126 generate aspectrally-resolved signal as a function of the detected wavelength.This spectrally-resolved signal contains the spectroscopic informationin the form of the cumulative absorbance of the sample illuminated bythe probe 106.

The cumulative absorbance of the sample can also be measured without areflector 121 in the system. To do so, one performs optical frequencydomain reflectometry to obtain the sub-surface imaging information fromthe spectrally-resolved signal. For example, the Fourier transform ofthe spectrally-resolved signal contains information about the locationof structural elements in the sample illuminated by the probe 106.

Measurement of a known sample with the VPDS 100B is useful as a baselinemeasurement (e.g., to calibrate the system). In some cases, the baselinesample is one with no spectral features in the range of interest.Alternatively, a sample with well-characterized spectral features in therange of interest can be used.

Referring to FIG. 1C, in a third embodiment, a VPDS 100C uses aMach-Zender Interferometer (MZI) topology for sub-surface imaging. TheVPDS 100C includes a first optical waveguide 108 and a second opticalwaveguide 114 each extending into the probe 106, and a third opticalwaveguide 118 coupled to a portion of the second optical waveguide 114via a first beamsplitter 152. The VPDS 100C also includes a fourthoptical waveguide 150 coupled to a portion of the first opticalwaveguide 108 via a second beamsplitter 154. Each of the first andsecond beamsplitters is a 50/50 fused-fiber 1×2 coupler with a 50% powersplitting ratio, one input port and two output ports, or equivalently,two input ports and one output port.

In the MZI topology, the first beamsplitter 152 splits the incominglight from the optical source 122 into two paths. Light in a“measurement path” propagates in the second optical waveguide 114 and istransformed (e.g., in amplitude and/or phase) by scattering from ameasurement object (the arterial wall 104 in this example). Thescattered light is collected into the first optical waveguide 108 viathe optical delivery and collection head 115 (FIG. 1A). Light in a“reference path” propagates in the third optical waveguide 118 toward avariable-delay coupler 156 that imparts a variable group delay to thelight before coupling the light back into the fourth optical waveguide150.

Light from the measurement path in the first optical waveguide 108 andthe light from the reference path in the fourth optical waveguide 150recombine in the second beamsplitter 154 to produce an interferencesignal at an optical detector 126. As in the MI topology, as the groupdelay of the reference path is scanned, the interference signal yieldsinformation from different depths of the measurement object according toa coherence envelope of a limited-coherence light source. As in VPDS100B, the processing module 140 can obtain sub-surface imaginginformation and spectroscopic information based on combined propertiesof, for example, the optical source 122, the optical coupler 128, andthe optical detector 126

Referring to FIG. 1D, in a fourth embodiment, a VPDS 100D includes afifth optical waveguide 160, an optical coupler 162, and an opticaldetector 164 for spectroscopic analysis, as in the VPDS 100A of thefirst embodiment, and uses a MZI topology for sub-surface imaging, as inthe VPDS 100C of the third embodiment. Other embodiments includingcombinations or variations of these four embodiments are possible.

Referring again to FIG. 1A, during operation, the probe 106 is insertedalong a blood vessel, typically an artery, using a guidewire (notshown). One using the VPDS 100A engages a motor 170 coupled to the probe106. The motor 170 rotates the probe 106 at a rate between approximately1 revolution per second and 400 revolutions per second. This causes theoptical delivery and collection head 115 to trace a path around theinner circumference of the arterial wall 104. In one practice the probe106 is inserted in discrete steps, with a complete rotation occurring ateach such step. In this case, the spectroscopic and sub-surface imagingdata can be collected along discrete circular paths. Alternatively, theprobe 106 is inserted continuously, with axial translation and rotationoccurring simultaneously. In this case, the spectroscopic andsub-surface imaging data are collected along continuous helical paths.

As it rotates, the optical delivery and collection head 115 redirectslight placed on one of the optical waveguides by the optical source 122to a scanning area 172. At the same time, the optical delivery andcollection head 115 collects light re-emerging from the scanning area172 and directs it into each optical waveguide in the probe that isconfigured to receive light for spectroscopic analysis and sub-surfaceimaging, as described above. The variable-delay reflector 120 orvariable-delay coupler 156 is configured to scan the variable opticalgroup delay by an amount corresponding to a coherence length of theoptical source 122.

The collected spectroscopic data can be used to generate athree-dimensional spectral map of the arterial wall 104, and thecollected sub-surface imaging data can be used to generate athree-dimensional morphological map of the arterial wall 104. Since thespectroscopic and sub-surface imaging data collected at a given timecorrespond to the same or similar region of the artery, the spectral mapand the morphological map can be easily co-registered to match specificspectral and morphological features. As the probe 106 traverses anartery, both the spectroscopic data and the sub-surface imaging data canbe used in real-time to diagnose vulnerable plaques, or identify otherlesion types that have properties that can be identified by these twodetection modalities. The probe 106 can optionally include structuresfor carrying out other diagnostic or treatment modalities in addition tothe infrared spectroscopy and sub-surface imaging diagnostic modalities.

The optical delivery and collection head 115 (FIG. 1A) includes one ormore light couplers in optical communication with distal ends of one ormore optical waveguides at the distal end 110 of the probe 106. Forexample, in embodiments in which optical radiation for sub-surfaceimaging is delivered from and collected back into the same opticalwaveguide (e.g., VPDS 100A and VPDS 100B), the probe 106 can includeonly one optical waveguide for delivery and collection with the sameoptical waveguide used to collect the optical radiation forspectroscopic analysis and sub-surface imaging. Such embodiments canalternatively include more than one optical waveguide for separatecollection of optical radiation for spectroscopic analysis andsub-surface imaging. In embodiments in which optical radiation forsub-surface imaging is delivered from one optical waveguide andcollected into another optical waveguide (e.g., VPDS 100C and VPDS100D), the probe 106 includes at least two optical waveguides.

The optical delivery and collection head 115 can use any of a variety oftechniques to transmit optical radiation between the optical waveguidesand the arterial wall. In some embodiments, the optical delivery andcollection head 115 includes an atraumatic light-coupler configured toatraumatically contact the arterial wall. Such an atraumaticlight-coupler can couple light directly without having to transmit thelight through intervening media such as blood, as described below.

In a first embodiment, shown in FIGS. 2-3, an atraumatic light-coupler224 at the distal end of the probe 216 rests on a contact area 226 onthe arterial wall 214. When disposed as shown in FIG. 2, the atraumaticlight-coupler 224 directs light traveling axially on the fiber 218 tothe contact area 226. After leaving the atraumatic light-coupler 224,this light crosses the arterial wall 214 and illuminates structures 228behind the wall 214. These structures 228 scatter some of the light backto the contact area 226, where it re-emerges through the arterial wall214. The atraumatic light-coupler 224 collects this re-emergent lightand directs it into the fiber 218.

Along a proximal section of the probe 216, as shown in FIG. 3, a rigidtube 238 encasing the fiber 218, enables the probe 216 to be pushedthrough the artery. Along a central and distal section of the probe 216,a coil wire 244 wound into a flexible coil-wire jacket 246 encases thefiber 218.

The coil wire 244 has a constant diameter along the central section.Along the distal section of the probe 216, the diameter of the coil wire244 becomes progressively smaller. As a result, the distal section ofthe probe 216 is more flexible than its central section. This enhancedflexibility enables the distal section to follow the contour of the wall214 without exerting unnecessary force against it.

The atraumatic light-coupler 224 can be formed by attaching a lensassembly to a distal tip of the fiber 218, as shown in FIGS. 4A, 4B, and4E, or by attaching a rounded glass tip to an angled fiber, as shown inFIGS. 4F-G. Alternatively, the atraumatic light-coupler 224 can be madeintegral with the fiber 218 by smoothing any sharp edges at its distaltip, as shown in FIGS. 4C-D.

In either case, the atraumatic light-coupler 224 can include a sphericallens, as shown in FIG. 4A, or a hemispherical lens, as shown in FIG. 4B.The atraumatic light-coupler 224 can also include more than one lenselement, as shown in FIG. 4E.

Alternatively, the atraumatic light-coupler 224 can be integral with thefiber 218. For example, the distal tip of the fiber 218 can be formedinto a plane having rounded edges and oriented at an angle relative tothe plane of the fiber cross-section, as shown in FIG. 4D, or into ahemisphere, as shown in FIG. 4C.

In a second embodiment, shown in FIGS. 5A-C, a probe housing 259 extendsthrough a cannula 260 parallel to, but radially displaced from alongitudinal axis thereof. A probe 216 is kept inside the probe housing259 until it is ready to be deployed. Extending along the longitudinalaxis of the cannula 260 is a guide-wire housing 261 forming a guide-wirelumen through which a guide-wire 263 extends.

The probe 216 includes one or more optical waveguides as in thevulnerable plaque detection systems 100A-100D described above. Forembodiments in which the same optical waveguide is used to collect thelight for spectroscopic analysis and sub-surface imaging (e.g., VPDS100B and VPDS 100C), an optical fiber made of glass or plastic can beused to collect the scattered light. For embodiments in which a separateoptical waveguide is used to collect light for spectroscopic analysis(e.g., VPDS 100A and VPDS 100D), the optical waveguide for spectroscopicanalysis can include an optical fiber made of glass or plastic, or abundle of such fibers. In one embodiment, the probe includes a bundle of25 optical fibers, each 0.005 millimeters in diameter. The fiber(s) canbe exposed, coated with a protective biocompatible layer and/or alubricious layer such as polytetrafluoroethylene (“PTFE”), or encased ina coil-wire jacket. The optional coating or jacket around the fiber(s)could be round, and hence bendable in all directions, or flat, so as tosuppress bending in undesired directions.

For embodiments in which a separate optical waveguide is used to collectlight for spectroscopic analysis (e.g., VPDS 100A and VPDS 100D), theoptical waveguide for spectroscopic analysis can alternatively includean annular waveguide of a double-clad fiber. A waveguide of this typeand a corresponding optical delivery and collection head 115 aredescribed filly in U.S. application Ser. No. 10/218,939 (Publication No.2004/0034290), the contents of which are herein incorporated byreference.

The distal tip of the optical fiber 218 is capped by any of theatraumatic light-couplers 224 discussed above. When the distal end ofthe cannula 260 is just proximal to contact area 226, the probe 216 ispushed distally so that its distal tip extends past the distal end ofthe cannula 260. Alternatively, the probe 216 remains stationary whilethe cannula 260 is retracted, thereby exposing the probe 216.

The probe 216 is pre-formed so that a natural bend urges it outward,away from the axis of the cannula 260. As a result, when the probe 216is extended out its housing 259 and beyond the distal end of the cannula260, this natural bend places the atraumatic light-coupler 224 of thefiber 218 in contact with the arterial wall 214 distal to the cannula260. The probe 216 is then rotated so that the atraumatic light-coupler224 traces out a circular contact path along an inner circumference ofthe wall 214, as shown in FIGS. 5A and 5C.

A variety of ways are known for pre-forming a probe 216. For example,the probe 216 can be heated while in the desired shape. Or a coatingover the fiber within the probe 216 can be applied and cured while thefiber is in the desired shape.

In a third embodiment, shown in FIGS. 5D-F, the cannula 260 has aproximal section 288 and a distal section 290 separated from each otherby a circumferential gap 292. A guide wall 294 forms a truncated coneextending distally from a truncated end joined to the guide-wire housing259 to a base joined to the distal section 290 of the cannula 260. Theguide wall 294 thus serves to maintain the position of the proximal anddistal sections 288, 290 of the cannula 260 relative to each other whilepreserving the circumferential gap 292 all the way around the cannula260.

In use, the probe 216 is extended distally toward the guide wall 294,which then guides the probe 216 out of the circumferential gap 262. Aswas the case with the second embodiment (FIGS. 5A-C), the natural bendof the probe 216 urges the atraumatic tip 224 into contact with thearterial wall 214. Once the probe's atraumatic tip 224 contacts the wall214, the probe 216 is rotated as shown in FIGS. 5D-F so that theatraumatic tip 224 sweeps a circumferential contact path on the arterialwall 214.

In a fourth embodiment, shown in FIGS. 6A-C, several probes 216 of thetype discussed above in connection with FIGS. 5A-F pass through thecannula 260 at the same time. Optional spacer rings 264 are attached tothe probes 262 at one or more points along their distal sections. Thespacer rings 264 can be silicon webbing, plastic, Nitinol, or any otherbiocompatible material.

When deployed, the spacer rings 264 are oriented so as to lie in a planeperpendicular to the longitudinal axis of the cannula 260. The spacerrings 264 thus maintain the relative positions of the probes 216 duringscanning of the wall 214. A multi-probe embodiment as shown in FIGS.6A-C enables most of the circumference of an arterial wall 214 to beexamined without having to rotate the probes 216.

In a fifth embodiment, shown in FIGS. 6D-F, the cannula 260 is asdescribed in connection with the third embodiment (FIGS. 5D-F). Thedifference between this fifth embodiment and the third embodiment (FIGS.5D-F) is that in the third embodiment, a single probe 216 extendsthrough the circumferential gap 292, whereas in this fifth embodiment,several probes 216 circumferentially offset from one another extendthrough the circumferential gap 292. As a result, in the thirdembodiment, it is necessary to rotate the probe 216 to inspect theentire circumference of the arterial wall 214, whereas in the fifthembodiment, one can inspect most of the arterial wall 214 circumferencewithout having to rotate the probes 216 at all.

In a sixth embodiment, a cannula 260 has a tapered distal end 268, asshown in FIG. 7A, or a flared distal end 270, as shown in FIG. 7B. Achannel 272 formed in the inner wall of the cannula 260 has a bend 274proximal to an opening 276 at the distal end. This opening 276 defines asurface whose normal vector has both a radial component and anlongitudinal component.

One operating the embodiments of FIGS. 7A and 7B pushes the probe 216through the channel 272, which then guides it toward the opening 272. Asthe probe 216 exits the channel 272, it proceeds in the direction of thenormal vector until its atraumatic light-coupler 224 contacts thearterial wall 214. In this case, the probe 216 need not be pre-formed tohave a preferred shape since the channel 272 guides the probe 216 in thecorrect direction for reaching the wall 214.

In a seventh embodiment, shown in FIGS. 8A-B, a plurality of probes 216passes through a cannula 260. The distal ends of the probes 216 areattached to anchor points circumferentially distributed around a hub278. The hub 278 is coupled to a control wire 280 that enables it to bemoved along the longitudinal axis of the cannula 260 to either deploythe probes 216 (FIG. 8A) or to retract the probes 216 (FIG. 8B).However, in other embodiments, the hub 278 remains stationary and it isthe cannula 260 that is moved proximally and distally to either deployor recover the probes 216.

The probes 216 are pre-formed to bow outward as shown in FIG. 8A so asto contact the arterial wall 214 at an intermediate point between thehub 278 and the cannula 260. Optional spacer rings 264, like thosediscussed in connection with FIGS. 6A-C, are attached to the probes 216at one or more points along their distal sections to maintain theirrelative positions. In this seventh embodiment, the atraumaticlight-coupler 224 includes a side-window 282 located at the intermediatepoint. The side window 282 faces radially outward so that when the probe216 is fully deployed, the side window 282 atraumatically contacts thearterial wall 214.

An atraumatic light-coupler 224 for placement along the side of theprobe 216 includes a right-angle reflector 284, such as a prism ormirror, placed in optical communication between the fiber 218 and theside window 282, as shown in FIG. 9B. Alternatively, an air gap 286 isplaced in optical communication between the tip of an angle polishedfiber 218 and the side-window 282, as shown in FIG. 9A.

FIGS. 9C-9D shows additional examples of atraumatic light-couplers 224for placement along the side of the probe 216. In these examples, theside window 282 is formed by a portion of the fiber's cladding that isthin enough to allow passage of light. The side window 282 can be leftexposed, as shown in FIG. 9C, or a diffraction grating 285 can be placedin optical communication with the side window 282 to further control thedirection of the beam, as shown in FIG. 9D.

When the hub 278 and the cannula 260 are drawn together, as shown inFIG. 8B, they can easily be guided to a location of interest. Once thehub 278 and cannula 260 reach a location of interest, one eitheradvances the hub 278 or retracts the cannula 260. In either case, theprobes 216 are released from the confines of the cannula 260, as shownin FIG. 8A. Once free of the radially restraining force applied by thecannula's inner wall, the probes 216 assume their natural shape, bowingoutward, as shown in FIG. 8B, so that their respective side-windows 282atraumatically contact the arterial wall 214. The atraumaticlight-couplers 224 guide light from the light source 250 through theside windows 282. At the same time, the atraumatic light-couplers 224recover re-emergent light from the wall 214 through the side windows 282and pass it into the fibers 218, which guide that light to an opticaldetector.

When the examination of the wall 214 is complete, the hub 278 andcannula 260 are brought back together, as shown in FIG. 8B, and theprobes 216 are once again confined inside the cannula 260.

In an eighth embodiment, shown in FIGS. 8C-D, the cannula 260 has aproximal section 288 and a distal section 290 separated by acircumferential gap 292, as described in connection with the thirdembodiment (FIGS. 5D-F) and the fifth embodiment (FIGS. 6D-F). Unlikethe third and fifth embodiments, in which the distal tips of the probes216 atraumatically contact the wall 214, in the eighth embodiment thedistal tips of the probes 216 are attached to a hub 278 at the distalsection 290 of the cannula 260. Like the probes 216 of the seventhembodiment, the probes 216 of the eighth embodiment have side windows 82at intermediate points for atraumatically contacting the arterial wall214. An actuator (not shown) is mechanically coupled to selectivelyapply tension to the probes 216. When the probes 216 are under tension,they lie against the distal section 290 of the cannula 260, as shown inFIG. 8D. When probes 216 are relaxed, they spring radially outward, awayfrom the distal section 290, enough so that the side windows 282 at theintermediate sections atraumatically contact the arterial wall 214.

In use, the cannula 260 is guided to a region of interest with theprobes 216 placed under tension. The probes 216 are thus drawn againstthe cannula 260, as shown in FIG. 8B. Once at the region of interest,the tension is released, and the probes 216 spring radially outward, asshown in FIG. 8A, so that the side windows 282 atraumatically contactthe wall 214. After data collection, the probes 216 are again placedunder tension to draw them back against the cannula 260, as shown inFIG. 8B.

In the seventh and eighth embodiments, a particular probe 216 emergesfrom the cannula 260 at an exit point and re-attaches to the hub 278 atan anchor point. In a cylindrical coordinate system centered on the axisof the cannula 260, the exit point and the anchor point have differentaxial coordinates but the same angular coordinate. However, as FIGS. 8Eand 8F illustrate, this need not be the case.

FIG. 8E shows a ninth embodiment in which a cannula 260 has a pluralityof exit holes 296 and a corresponding plurality of entry holes 298. Eachprobe 216 exits the cannula 260 through an exit hole 296 and re-entersthe cannula 260 through an entry hole 296 that is circumferentiallyoffset from its corresponding exit hole. This results in the helicalarrangement shown in FIG. 8E. The extent of the circumferential offsetdefines the pitch of the helix.

The distal ends of the probe 216 are attached to a hub 278 (not shown)inside the cannula 260. Each probe 216 has a side window 282 between theexit hole and the corresponding entry hole. A control wire 280 withinthe cannula 260 (not shown) deploys the probes 216, as shown, orretracts them so that they rest against the exterior of the cannula 260.A guide-wire 263 passing through the cannula 260 and exiting out thedistal tip thereof enables the cannula 260 to be guided to a region ofinterest.

FIG. 8F shows a tenth embodiment in which a cannula 260 has a distalsection 288 and a proximal section 290. The proximal and distal sectionsof the cannula 260 surround a central shaft 300 having an exposedportion 302. Probes 216 extend axially through a gap between the shaftand the cannula 260. The probes 216 are anchored at their distal ends atcircumferentially displaced anchor points on a hub 278 attached to theshaft 300. The circumferential offset causes the helical configurationof the probes 216 in FIG. 8F. The extent of this circumferential offsetdefines a pitch of the helix.

An actuator (not shown) selectively applies tension to the probes 216.When the probes 216 are under tension, they retract against the exposedportion 302 of the central shaft 300. When the probes 216 are relaxed,they assume the configuration shown in FIG. 8F, in which they springradially outward from the exposed portion 302 of the central shaft 300so that their side windows 282 atraumatically contact the arterial wall214.

In the embodiments described thus far, the probes 216 and the cannula260 have been separate structures. However, the probes 216 can also beintegrated, or otherwise embedded in the cannula 260. In this case,portions of the cannula 260 extend radially outward to contact thearterial wall 214.

FIGS. 8G and 8H show an eleventh embodiment in a deployed and retractedstate, respectively. The eleventh embodiment includes slots 304 cut intothe wall of the cannula 260 enclosing an internal shaft 300. Pairs ofadjacent slots 304 define probe portions 216 of the cannula 260. Theprobe portions 216 buckle outward when the distal tip of the cannula 260is pulled proximally, as shown in FIG. 8G. When the distal tip of thecannula 260 is extended, the probe portions 216 lay flat against theshaft 300, as shown in FIG. 8H.

Each probe portion 216 has a side window 282 for atraumaticallycontacting the wall 214 when the probe portion 216 is deployed. The sidewindow 282 is in optical communication with an atraumatic coupler 224.An optical fiber embedded within the wall of the cannula 260 provides anoptical path to and from the atraumatic coupler 224.

FIGS. 8I-J show a twelfth embodiment in a deployed and retracted state.The twelfth embodiment includes slots 304 cut into the wall of thecannula 260 enclosing an internal shaft 300. Unlike the slots 304 in theeleventh embodiment, the slots 304 in the twelfth embodiment extend allthe way to the distal tip of the cannula. Pairs of adjacent slots 304define probe portions 216 of the cannula 260.

As shown in the cross-section of FIG. 8K, the cannula 260 includesradially-inward projections 306 forming a throat 310. The shaft 100 hasa bulbous portion 312 distal to the throat 310 and a straight portion314 extending proximally through the throat 310 to join the bulbousportion 312. The probe portions 216 are biased to rest against thebulbous portion 312 of the shaft 300, as shown in FIG. 8I. When theshaft 300 is drawn proximally, the bulbous portion 312 wedges againstthe projections 306. This forces the probe-portions 216 to pivotradially outward, as shown in FIG. 8J.

Each probe portion 216 has an atraumatic coupler 224 at its distal tipfor atraumatically contacting the wall 214 when the probe portion 216 isdeployed. An optical fiber embedded within the wall of the cannula 260provides an optical path to and from the atraumatic coupler 224.

The optical delivery and collection head 115 can use other techniques totransmit optical radiation between the optical waveguides and thearterial wall. In some embodiments, the optical delivery and collectionhead 115 includes one or more beam redirectors.

FIG. 10 shows an optical bench 348 in which are seated the collectionfiber 320 and the delivery fiber 318. The optical bench 348 is seated ina recess 350 between first and second side walls 352A-B of the distalend of a housing 354. The housing 354 is in turn coupled to the distalend of the torque cable 328. The recess 350 is just wide enough toenable the collection fiber 320 and the delivery fiber 318 to nestleadjacent to each other. A floor 356 extending between the first andsecond side walls 352A-B and across the recess 350 supports both thecollection and delivery fibers 318, 320.

Just distal to the end of the delivery fiber 318, a portion of theoptical bench 348 forms a frustum 358. The frustum 358 extendstransversely only half-way across the optical bench 48, thereby enablingthe collection fiber 320 to extend distally past the end of the deliveryfiber 318.

The frustum 358 has an inclined surface facing the distal end of thedelivery fiber 318 and a vertical surface facing the distal end of theoptical bench 348. The inclined surface forms a 135 degree anglerelative to the floor 356. However, other angles can be selecteddepending on the direction in which light from the delivery fiber 318 isto be directed. A reflective material coating the inclined surface formsa beam redirector, which in this case is a delivery mirror 360. Whenlight exits axially from the delivery fiber 318, the delivery mirror 360intercepts that light and redirects it radially outward to the arterialwall 214. Examples of other beam redirectors include prisms, lenses,diffraction gratings, and combinations thereof.

The collection fiber 320 extends past the end of the delivery fiber 318until it terminates at a plane that is coplanar with the vertical faceof the frustum 358. Just beyond the distal end of the collection fiber320, a portion of the optical bench 348 forms an inclined surfaceextending transversely across the optical bench 348 and making an anglegreater than 135 degrees relative to the floor 356. A reflectivematerial coating the inclined surface forms a collection mirror 382.

A delivery-fiber stop 386 molded into the optical bench 348 proximal tothe frustum 358 facilitates placement of the delivery fiber 318 at adesired location proximal to the delivery mirror 360. Similarly, acollection-fiber stop 388 molded into the optical bench 348 justproximal to the collection mirror 382 facilitates placement of thecollection fiber 320 at a desired location proximal to the collectionmirror 382.

Other types of beam redirecting techniques are possible including anycombination of techniques described fully in U.S. Pat. No. 6,654,630 andU.S. Pat. No. 6,701,181, the contents of which are herein incorporatedby reference.

OTHER EMBODIMENTS

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Otheraspects, advantages, and modifications are within the scope of thefollowing claims.

1. An apparatus for detecting vulnerable plaque within a lumen definedby an intraluminal wall, the apparatus comprising: a probe having adistal portion and a proximal portion; an optical waveguide extendingalong the probe, the optical waveguide being configured to carry opticalradiation between the distal and proximal portions, and having a distalend in communication with the intraluminal wall; an interferometercoupled to the optical waveguide and configured to provide aninterference signal for sub-surface imaging of the intraluminal wall; aprocessing module configured to provide spectroscopic information aboutthe intraluminal wall from detected intensity of light collected fromthe intraluminal wall; and an optical source configured to coupleoptical radiation into the optical waveguide, wherein the optical sourceis configured to emit narrowband optical radiation scanned over a rangeof wavelengths to form the interference signal for sub-surface imagingand the spectroscopic information provided from the detected intensityof light collected from the intraluminal wall.
 2. The apparatus of claim1, wherein the processing module is configured to receive the detectedintensity of light collected from the intraluminal wall by the opticalwaveguide.
 3. The apparatus of claim 1, further comprising: a secondoptical waveguide extending along the probe, the second opticalwaveguide being configured to carry optical radiation between the distaland proximal portions, and having a distal end in communication with theintraluminal wall.
 4. The apparatus of claim 3, wherein the processingmodule is configured to receive the detected intensity of lightcollected from the intraluminal wall by the second optical waveguide. 5.The apparatus of claim 1, wherein the interferometer is configured toprovide an interference signal for sub-surface imaging by performingoptical coherence tomography.
 6. The apparatus of claim 1, wherein theinterferometer is configured to provide an interference signal forsub-surface imaging by performing optical frequency domainreflectometry.
 7. The apparatus of claim 1, wherein the processingmodule is configured to provide a cumulative absorbance over aparticular thickness of the intraluminal wall from the detectedintensity of light collected from the intraluminal wall.
 8. Theapparatus of claim 1, wherein the optical waveguide has a distal end incommunication with the intraluminal wall through an atraumaticlight-coupler configured to atraumatically contact the intraluminalwall.
 9. An apparatus for detecting vulnerable plaque within a lumendefined by an intraluminal wall, the apparatus comprising: a probehaving a distal portion and a proximal portion; a first opticalwaveguide extending along the probe, the first optical waveguide beingconfigured to carry optical radiation between the distal and proximalportions, and having a distal end in communication with an area of theintraluminal wall; a second optical waveguide extending along the probe,the second optical waveguide being configured to carry optical radiationbetween the distal and proximal portions, and having a distal end incommunication with the area of the intraluminal wall; a third opticalwaveguide coupled to a portion of the second optical waveguide; a fourthoptical waveguide coupled to a portion of the first optical waveguide:an optical source configured to couple optical radiation into the secondand third optical waveguides; a variable-delay coupler configured tocouple optical radiation from the third optical waveguide into thefourth optical waveguide with a variable optical group delay, whereinthe variable-delay coupler is configured to scan the variable opticalgroup delay by an amount corresponding to a coherence length of a sourceof optical radiation, and an optical detector configured to receiveoptical radiation from the first and fourth optical waveguides.
 10. Theapparatus of claim 9, further comprising: an optical coupler in opticalcommunication with the distal end of the first optical waveguide, theoptical coupler being configured to transmit optical radiation betweenthe first optical waveguide and the intraluminal wall.
 11. The apparatusof claim 10, wherein the optical coupler comprises an atraumaticlight-coupler configured to atraumatically contact the intraluminalwall.
 12. The apparatus of claim 9, further comprising: an opticalcoupler in optical communication with the distal end of the secondoptical waveguide, the optical coupler being configured to transmitoptical radiation between the second optical waveguide and theintraluminal wall.
 13. The apparatus of claim 9, wherein the secondoptical waveguide is configured to provide light to the intraluminalwall, and the third optical waveguide is configured to provide referencelight that is combined with light from the first optical waveguidecollected from the intraluminal wall to provide an interference signalfor sub-surface imaging of the intraluminal wall.
 14. The apparatus ofclaim 9, further comprising: an optical coupler in optical communicationwith the distal end of the first optical waveguide and the distal end ofthe second optical waveguide, the optical coupler being configured totransmit optical radiation from the second optical waveguide to theintraluminal wall and from the intraluminal wall to the first opticalwaveguide.
 15. A method for detecting vulnerable plaque within a lumendefined by an intraluminal wall, the method comprising: inserting adistal portion of a probe into the lumen; providing optical radiation tothe intraluminal wall through an optical waveguide extending along theprobe; combining reference optical radiation with optical radiationscattered from the intraluminal wall, and returning through the opticalwaveguide, to provide an interference signal for sub-surface imaging ofthe intraluminal wall; processing a detected intensity of lightcollected from the intraluminal wall to extract spectroscopicinformation; generating a morphological map of the intraluminal wallbased on the interference signal; generating a spectral map of theintraluminal wall based on the spectroscopic information; andco-registering portions of the morphological map and the spectral mapcollected at a given time corresponding to a given portion of theintraluminal wall.
 16. An apparatus for detecting vulnerable plaguewithin a lumen defined by an intraluminal wall, the apparatuscomprising: a probe having a distal portion and a proximal portion; anoptical waveguide extending along the probe, the optical waveguide beingconfigured to carry optical radiation between the distal and proximalportions, and having a distal end in communication with the intraluminalwall through an atraumatic light-coupler configured to atraumaticallycontact the intraluminal wall; an interferometer coupled to the opticalwaveguide and configured to provide an interference signal forsub-surface imaging of the intraluminal wall; a processing moduleconfigured to provide spectroscopic information about the intraluminalwall from detected intensity of light collected from the intraluminalwall; and an optical source configured to couple optical radiation intothe optical waveguide, wherein the optical source is configured to emitbroadband optical radiation that includes a range of wavelengths to formthe interference signal for sub-surface imaging and the spectroscopicinformation provided from the detected intensity of light collected fromthe intraluminal wall.
 17. The apparatus of claim 1, wherein the opticalwaveguide has a distal end in communication with the intraluminal wallthrough an atraumatic light-coupler configured to atraumatically contactthe intraluminal wall.